1. Field of the Invention
This invention relates generally to an automatic transmission for a motor vehicle, and, more particularly, to a method for establishing a gear shift schedule that is compatible with driving behavior.
2. Description of the Prior Art
Gear changes in a step-change automatic transmission are produced by a shift control system when a current operating state, defined by throttle opening and vehicle speed, crosses an upshift or downshift boundary, which can be represented in a shift schedule graph. The shift control system controls a solenoid valves of a hydraulic system such that hydraulic pressure, supplied to friction clutches and brakes, alternately cause their engagement and disengagement, resulting in the shifting of the transmission into various gears that affect the speed of the transmission output shaft relative to the speed of the input shaft.
The vehicle operator's manual control of a shift lever can be used to select operation of the transmission in a normal range, wherein the gears are produced automatically. The shift lever can also be placed in a track for manual gear selection, wherein the transmission can be upshifted and downshifted from the current gear at the driver's initiative. The shift control responds to the manual selection in a manner that is similar to its operation in the automatic mode.
The shift control system may contain multiple shift schedules each producing a desired gear change timing in a range between conservative or economy operation of the vehicle and aggressive or sporty operation, usually represented by throttle opening, i.e., the degree to which an accelerator pedal is depressed, and vehicle speed.
In the economy mode, a gear shift pattern is designed such that an upshifting operation is quickly realized to improve the fuel consumption ratio. In the sporty mode, a shift pattern is designed such that an upshifting point is moved to a high speed so that engine torque can be increased.
However, since the shift schedules are fixed in an electronic memory, a need exists in the industry to optimize the gear shifting according to variations in engine torque, and running resistance and other parameters that reflect the operator's intent and driving behavior.